Optically read and written memory devices have the potential of providing a significant advance in the data storage capacity of computer systems and the like. In principle, data storage capacities of the order of 10.sup.12 bits/m.sup.2 of storage media are possible with such devices. However, in spite of intense research and development work, optical read/write memories based on existing technologies are at best a marginal improvement over conventional magnetic memories.
The most attractive of the currently available read/write optical disks are based on magneto-optic materials. These disks have latency times of about 100 ms and may be rewritten only about 10.sup.4 times. For comparison, conventional magnetic hard disks used in computer systems may be rewritten more than 10.sup.6 times and have latency times less than 20 ms. In addition to poor latency times and insufficient rewrite capability, the intensity of laser light required to store the information in magneto-optical media is of the order of 10.sup.5 watts/cm.sup.2. This high intensity results from the need to thermally alter the phase of the magneto-optical media. To operate at these power densities, the laser diode used to write the magneto-optical media must operate near saturation. As a result, the life-time of the laser diode is significantly reduced.
In addition to requiring that the laser diodes be run near saturation, much larger area laser diodes must be used. The light from the diode is then concentrated on the appropriate location in the storage media. This concentration operation requires a long focal length lens which places a lower limit on the distance between the laser diode and the surface of the storage medium. This distance complicates the task of tracking on the disk, and limits the density of data that can be stored on such a disk.
Accordingly, it is an object of the present invention to provide an improved read/write optical disk.
It is a further object of the present invention to provide a read/write optical disk with lower latency times than currently available read/write optical disks.
It is yet another object of the present invention to provide a read/write optical disk which can be rewritten as many times as currently available magnetic hard disks.
It is a still further object of the present invention to provide a read/write optical disk which requires less power to write then prior art read/write optical disks.
It is a yet another object of the present invention to provide a read/write optical disk with a lighter weight reading mechanism than that of prior art read/write optical disks.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.